Channel estimation for two-stage sidelink control using sidelink data channel dmrs

ABSTRACT

Certain aspects of the present disclosure provide techniques for channel estimation for two-stage sidelink control using sidelink data channel demodulation reference signals (DMRS). A user equipment (UE) can transmit DMRS for the sidelink data channel. The UE may transmit the second stage of the sidelink control using antenna ports or a precoder used for the sidelink data channel. The receiving device may receive the DMRS, estimate the channel, and demodulate the second stage of the sidelink control based on the estimated channel. The receiving device may flexibly determine the DMRS to use for the estimation and demodulation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit to Greece Patent Application Serial No.20190100437, entitled “Channel Estimation for Two-Stage Sidelink ControlUsing Sidelink Data Channel DMRS,” filed Oct. 4, 2019, and assigned tothe assignee hereof, the contents of which are hereby incorporated byreference in its entirety.

BACKGROUND Field of the Disclosure

Aspects of the present disclosure relate to wireless communications, andmore particularly, to techniques for channel estimation for two-stagesidelink control using sidelink data channel demodulation referencesignals (DMRSs).

Description of Related Art

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,broadcasts, etc. These wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power, etc.). Examples of such multiple-access systems include3rdGeneration Partnership Project (3GPP) Long Term Evolution (LTE)systems, LTE Advanced (LTE-A) systems, code division multiple access(CDMA) systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, orthogonal frequency divisionmultiple access (OFDMA) systems, single-carrier frequency divisionmultiple access (SC-FDMA) systems, and time division synchronous codedivision multiple access (TD-SCDMA) systems, to name a few.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. New radio (e.g., 5G NR) is an exampleof an emerging telecommunication standard. NR is a set of enhancementsto the long term evolution (LTE) mobile standard promulgated by 3GPP. NRis designed to better support mobile broadband Internet access byimproving spectral efficiency, lowering costs, improving services,making use of new spectrum, and better integrating with other openstandards using OFDMA with a cyclic prefix (CP) on the downlink (DL) andon the uplink (UL). To these ends, NR supports beamforming,multiple-input multiple-output (MIMO) antenna technology, and carrieraggregation.

However, as the demand for mobile broadband access continues toincrease, there exists a need for further improvements in NR and LTEtechnology. Preferably, these improvements should be applicable to othermulti-access technologies and the telecommunication standards thatemploy these technologies.

SUMMARY

The systems, methods, and devices of the disclosure each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this disclosure as expressedby the claims that follow, some features will now be discussed briefly.After considering this discussion, and particularly after reading thesection entitled “Detailed Description” one will understand how thefeatures of this disclosure provide advantages that include improvedsidelink feedback transmission in resource pool.

One or more innovative aspects of the subject matter described in thisdisclosure can be implemented in a method for wireless communication bya user equipment (UE). The method generally includes receiving one ormore demodulation reference signals (DMRSs) for a sidelink data channeltransmission via a set of one or more antenna ports. The methodgenerally includes receiving a second stage of a two-stage sidelinkcontrol information (SCI) transmission using antenna ports from the setof antenna ports. The method generally includes demodulating the secondstage of the two-stage SCI using the one or more DMRSs for the sidelinkdata channel.

One or more innovative aspects of the subject matter described in thisdisclosure can be implemented in a method for wireless communication bya UE. The method generally includes receiving one or more DMRSs for aprecoded sidelink data channel transmission. The method generallyincludes estimating the channel based on the precoded sidelink datachannel transmission. The method generally includes demodulating asecond stage of a two-stage SCI transmission based on the estimation.

One or more innovative aspects of the subject matter described in thisdisclosure can be implemented in a method for wireless communication bya UE. The method generally includes receiving one or more DMRSs for asidelink data channel transmission in a slot via a set of one or moreantenna ports. The method generally includes flexibly determining DMRSsof the one or more DMRSs to use for demodulating a second stage of atwo-stage SCI transmission. The method generally includes demodulatingthe second stage of the two-stage SCI using the determined DMRSs for thesidelink data channel.

One or more innovative aspects of the subject matter described in thisdisclosure can be implemented in a method for wireless communication bya UE. The method generally includes transmitting one or more DMRSs for asidelink data channel transmission via a set of one or more antennaports. The method generally includes transmitting a second stage of atwo-stage SCI transmission using antenna ports from the set of antennaports.

One or more innovative aspects of the subject matter described in thisdisclosure can be implemented in a method for wireless communication bya UE. The method generally includes transmitting one or more DMRSs for asidelink data channel transmission, the sidelink data channel precodedwith a precoder. The method generally includes precoding a second stageof a two-stage SCI transmission using the precoder. The method generallyincludes transmitting the precoded second stage of the two-stage SCI.

Aspects of the present disclosure provide means for, apparatus,processors, and computer-readable mediums for performing the methodsdescribed herein.

To the accomplishment of the foregoing and related ends, the one or moreaspects comprise the features hereinafter fully described andparticularly pointed out in the claims. The following description andthe appended drawings set forth in detail certain illustrative featuresof the one or more aspects. These features are indicative, however, ofbut a few of the various ways in which the principles of various aspectsmay be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description,briefly summarized above, may be had by reference to aspects, some ofwhich are illustrated in the drawings.

It is to be noted, however, that the appended drawings illustrate onlycertain typical aspects of this disclosure and are therefore not to beconsidered limiting of its scope, for the description may admit to otherequally effective aspects.

FIG. 1 is a block diagram conceptually illustrating an exampletelecommunications system, in accordance with certain aspects of thepresent disclosure.

FIG. 2 is a block diagram conceptually illustrating a design of anexample a base station (BS) and user equipment (UE), in accordance withcertain aspects of the present disclosure.

FIG. 3A and FIG. 3B show diagrammatic representations of example vehicleto everything (V2X) systems, in accordance with certain aspects of thepresent disclosure.

FIG. 4 is a diagram illustrating example sidelink data demodulationreference signal (DMRS) and two-stage sidelink control information (SCI)transmission in a slot, in accordance with certain aspects of thepresent disclosure.

FIG. 5 is a flow diagram illustrating example operations by a UE forsecond stage SCI transmission with shared DMRS ports, in accordance withcertain aspects of the present disclosure.

FIG. 6 is a flow diagram illustrating example operations by a UE forsecond stage SCI demodulation with shared DMRS ports, in accordance withcertain aspects of the present disclosure.

FIG. 7 is a flow diagram illustrating example operations by a UE forsecond stage SCI transmission with shared sidelink data channelprecoder, in accordance with certain aspects of the present disclosure.

FIG. 8 is a flow diagram illustrating example operations by a UE forsecond stage SCI demodulation with shared sidelink data channelprecoder, in accordance with certain aspects of the present disclosure.

FIG. 9 is a flow diagram illustrating example operations by a UE forflexible DMRS determination for second stage SCI demodulation, inaccordance with certain aspects of the present disclosure.

FIG. 10 is a message flow diagram illustrating an example of messagesexchanged between a UE and a receiving device for DMRS and two-stage SCItransmission, in accordance with certain aspects of the presentdisclosure.

FIG. 11 illustrates a communications device that may include variouscomponents configured to perform operations for the techniques disclosedherein in accordance with aspects of the present disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in one aspectmay be beneficially utilized on other aspects without specificrecitation.

DETAILED DESCRIPTION

Aspects of the present disclosure provide apparatus, methods, processingsystems, and computer readable mediums for channel estimation fortwo-stage sidelink control using sidelink data channel demodulationreference signals (DMRS). Generally, as discussed in further detailbelow, two-stage sidelink control may include a first stage and a secondstage, where the second stage can be decoded (e.g., using a DMRS) todetermine whether the sidelink control transmission is intended for aspecific receiving device. As will be described, the techniquespresented herein allow demodulation of the second stage of a two stagesidelink control information (SCI) using the DMRS of the physicalsidelink shared channel (PSSCH), even when the SCI and PSSCH have adifferent number of layers (e.g., when the SCI and other information onthe PSSCH are transmitted using different numbers of layers).

The following description provides examples of channel estimation fortwo-stage sidelink control using sidelink data channel DMRS that may beused for sidelink in communication systems, and is not limiting of thescope, applicability, or examples set forth in the claims. Changes maybe made in the function and arrangement of elements discussed withoutdeparting from the scope of the disclosure. Various examples may omit,substitute, or add various procedures or components as appropriate. Forinstance, the methods described may be performed in an order differentfrom that described, and various steps may be added, omitted, orcombined. Also, features described with respect to some examples may becombined in some other examples. For example, an apparatus may beimplemented or a method may be practiced using any number of the aspectsset forth herein. In addition, the scope of the disclosure is intendedto cover such an apparatus or method that is practiced using otherstructure, functionality, or structure and functionality in addition to,or other than, the various aspects of the disclosure set forth herein.It should be understood that any aspect of the disclosure disclosedherein may be embodied by one or more elements of a claim. The word“exemplary” is used herein to mean “serving as an example, instance, orillustration.” Any aspect described herein as “exemplary” is notnecessarily to be construed as preferred or advantageous over otheraspects.

In general, any number of wireless networks may be deployed in a givengeographic area. Each wireless network may support a particular radioaccess technology (RAT) and may operate on one or more frequencies. ARAT may also be referred to as a radio technology, an air interface,etc. A frequency may also be referred to as a carrier, a subcarrier, afrequency channel, a tone, a subband, etc. Each frequency may support asingle RAT in a given geographic area in order to avoid interferencebetween wireless networks of different RATs.

The techniques described herein may be used for various wirelessnetworks and radio technologies me. For clarity, while aspects may bedescribed herein using terminology commonly associated with 3G, 4G,and/or new radio (e.g., 5G NR) wireless technologies, aspects of thepresent disclosure can be applied in other generation-basedcommunication systems.

NR access may support various wireless communication services, such asenhanced mobile broadband (eMBB) targeting wide bandwidth (e.g., 80 MHzor beyond), millimeter wave (mmW) targeting high carrier frequency(e.g., 25 GHz or beyond), massive machine type communications MTC (mMTC)targeting non-backward compatible MTC techniques, and/or missioncritical targeting ultra-reliable low-latency communications (URLLC).These services may include latency and reliability requirements. Theseservices may also have different transmission time intervals (TTI) tomeet respective quality of service (QoS) requirements. In addition,these services may co-exist in the same subframe.

Certain wireless networks utilize orthogonal frequency divisionmultiplexing (OFDM) on the downlink and single-carrier frequencydivision multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partitionthe system bandwidth into multiple (K) orthogonal subcarriers, which arealso commonly referred to as tones, bins, etc. Each subcarrier may bemodulated with data. In general, modulation symbols are sent in thefrequency domain with OFDM and in the time domain with SC-FDM. Thespacing between adjacent subcarriers may be fixed, and the total numberof subcarriers (K) may be dependent on the system bandwidth. The systembandwidth may also be partitioned into subbands.

5G NR may utilize OFDM with a cyclic prefix (CP) on the uplink anddownlink and include support for half-duplex operation using timedivision duplexing (TDD). A subframe can be 1 ms, but the basictransmission time interval (TTI) may be referred to as a slot. Asubframe contains a variable number of slots (e.g., 1, 2, 4, 8, 16, . .. slots) depending on the subcarrier spacing (SCS). The NR resourceblock (RB) may be 12 consecutive frequency subcarriers. NR may support abase SCS of 15 KHz and other subcarrier spacing may be defined withrespect to the base SCS, for example, 30 kHz, 60 kHz, 120 kHz, 240 kHz,etc. The symbol and slot lengths scale with the SCS. The CP length alsodepends on the SCS. 5G NR may also support beamforming and beamdirection may be dynamically configured. Multiple-input multiple-output(MIMO) transmissions with precoding may also be supported. In someexamples, MIMO configurations in the DL may support up to 8 transmitantennas with multi-layer DL transmissions up to 8 streams and up to 2streams per UE. In some examples, multi-layer transmissions with up to 2streams per UE may be supported. Aggregation of multiple cells may besupported with up to 8 serving cells.

FIG. 1 illustrates an example wireless communication network 100 inwhich aspects of the present disclosure may be performed. For example,the wireless communication network 100 may be an NR system (e.g., a 5GNR network).

As illustrated in FIG. 1, the wireless communication network 100 mayinclude a number of base stations (BSs) 110 a-z (each also individuallyreferred to herein as BS 110 or collectively as BSs 110) and othernetwork entities. A BS 110 may provide communication coverage for aparticular geographic area, sometimes referred to as a “cell”, which maybe stationary or may move according to the location of a mobile BS 110.In some examples, the BSs 110 may be interconnected to one anotherand/or to one or more other BSs or network nodes (not shown) in wirelesscommunication network 100 through various types of backhaul interfaces(e.g., a direct physical connection, a wireless connection, a virtualnetwork, or the like) using any suitable transport network. In theexample shown in FIG. 1, the BSs 110 a, 110 b and 110 c may be macro BSsfor the macro cells 102 a, 102 b and 102 c, respectively. The BS 110 xmay be a pico BS for a pico cell 102 x. The BSs 110 y and 110 z may befemto BSs for the femto cells 102 y and 102 z, respectively. A BS maysupport one or multiple cells. The BSs 110 communicate with userequipment (UEs) 120 a-y (each also individually referred to herein as UE120 or collectively as UEs 120) in the wireless communication network100. The UEs 120 (e.g., 120 x, 120 y, etc.) may be dispersed throughoutthe wireless communication network 100, and each UE 120 may bestationary or mobile.

According to certain aspects, the UEs 120 may be configured for sidelinkcommunications. As shown in FIG. 1, the UE 110 a includes a SCI manager122 a and the UE 120 b includes a SCI manager 122 b. The SCI manager 122a and/or the SCI manager 122 b may be configured to transmit and/orreceive/demodulate a two-stage SCI, in accordance with aspects of thepresent disclosure. As discussed in more detail below, the SCI manager122 a and/or the SCI manager 122 b may transmit/demodulate a secondstage of the two-stage SCI using a shared DMRS port or shared precoder.As also discussed in more detail below, the SCI manager 122 a and/or theSCI manager 122 b may flexibly determine the DMRS used to demodulate thesecond stage of the two-stage SCI.

Wireless communication network 100 may also include relay stations(e.g., relay station 110 r), also referred to as relays or the like,that receive a transmission of data and/or other information from anupstream station (e.g., a BS 110 a or a UE 120 r) and sends atransmission of the data and/or other information to a downstreamstation (e.g., a UE 120 or a BS 110), or that relays transmissionsbetween UEs 120, to facilitate communication between devices.

A network controller 130 may couple to a set of BSs 110 and providecoordination and control for these BSs 110. The network controller 130may communicate with the BSs 110 via a backhaul. The BSs 110 may alsocommunicate with one another (e.g., directly or indirectly) via wirelessor wireline backhaul.

FIG. 2 illustrates example components of BS 110 a and UE 120 a (e.g., inthe wireless communication network 100 of FIG. 1, which may be similarcomponents in the UE 120 b), which may be used to implement aspects ofthe present disclosure.

At the BS 110 a, a transmit processor 220 may receive data from a datasource 212 and control information from a controller/processor 240. Thecontrol information may be for the physical broadcast channel (PBCH),physical control format indicator channel (PCFICH), physical hybrid ARQindicator channel (PHICH), physical downlink control channel (PDCCH),group common PDCCH (GC PDCCH), etc. The data may be for the physicaldownlink shared channel (PDSCH), etc. A medium access control(MAC)-control element (MAC-CE) is a MAC layer communication structurethat may be used for control command exchange between wireless nodes.For example, a BS may transmit a MAC CE to a UE to put the UE into adiscontinuous reception (DRX) mode to reduce the UE's power consumption.The MAC-CE may be carried in a shared channel such as a physicaldownlink shared channel (PDSCH), a physical uplink shared channel(PUSCH), or a physical sidelink shared channel. A MAC-CE may also beused to communicate information that facilitates communication, such asinformation regarding buffer status and available power headroom.

The processor 220 may process (e.g., encode and symbol map) the data andcontrol information to obtain data symbols and control symbols,respectively. The transmit processor 220 may also generate referencesymbols, such as for the primary synchronization signal (PSS), secondarysynchronization signal (SSS), and channel state information referencesignal (CSI-RS). A transmit (TX) multiple-input multiple-output (MIMO)processor 230 may perform spatial processing (e.g., precoding) on thedata symbols, the control symbols, and/or the reference symbols, ifapplicable, and may provide output symbol streams to the modulators(MODs) 232 a-232 t. Each modulator 232 may process a respective outputsymbol stream (e.g., for OFDM, etc.) to obtain an output sample stream.Each modulator may further process (e.g., convert to analog, amplify,filter, and upconvert) the output sample stream to obtain a downlinksignal. Downlink signals from modulators 232 a-232 t may be transmittedvia the antennas 234 a-234 t, respectively.

At the UE 120 a, the antennas 252 a-252 r may receive the downlinksignals from the BS 110 a and may provide received signals to thedemodulators (DEMODs) in transceivers 254 a-254 r, respectively. Eachdemodulator 254 may condition (e.g., filter, amplify, downconvert, anddigitize) a respective received signal to obtain input samples. Eachdemodulator may further process the input samples (e.g., for OFDM, etc.)to obtain received symbols. A MIMO detector 256 may obtain receivedsymbols from all the demodulators 254 a-254 r, perform MIMO detection onthe received symbols if applicable, and provide detected symbols. Areceive processor 258 may process (e.g., demodulate, deinterleave, anddecode) the detected symbols, provide decoded data for the UE 120 a to adata sink 260, and provide decoded control information to acontroller/processor 280.

On the uplink, at UE 120 a, a transmit processor 264 may receive andprocess data (e.g., for the physical uplink shared channel (PUSCH)) froma data source 262 and control information (e.g., for the physical uplinkcontrol channel (PUCCH) from the controller/processor 280. The transmitprocessor 264 may also generate reference symbols for a reference signal(e.g., for the sounding reference signal (SRS)). The symbols from thetransmit processor 264 may be precoded by a TX MIMO processor 266 ifapplicable, further processed by the demodulators in transceivers 254a-254 r (e.g., for SC-FDM, etc.), and transmitted to the BS 110 a. Atthe BS 110 a, the uplink signals from the UE 120 a may be received bythe antennas 234, processed by the modulators 232, detected by a MIMOdetector 236 if applicable, and further processed by a receive processor238 to obtain decoded data and control information sent by the UE 120 a.The receive processor 238 may provide the decoded data to a data sink239 and the decoded control information to the controller/processor 240.

The memories 242 and 282 may store data and program codes for BS 110 aand UE 120 a, respectively. A scheduler 244 may schedule UEs for datatransmission on the downlink and/or uplink.

The controller/processor 280 and/or other processors and modules at theUE 120 a may perform or direct the execution of processes for thetechniques described herein. For example, as shown in FIG. 2, thecontroller/processor 280 of the UE 120 a has a SCI manager 222 that maybe configured for channel estimation for two-stage SCI using sidelinkdata channel DMRS, in accordance with aspects of the present disclosure.Although shown at the controller/processor, other components of the UE120 a may be used to perform the operations described herein.

In some examples, access to the air interface may be scheduled. Ascheduling entity (e.g., a BS 110) allocates resources for communicationamong some or all devices and equipment within its service area or cell.The scheduling entity may be responsible for scheduling, assigning,reconfiguring, and releasing resources for one or more subordinateentities. That is, for scheduled communication, subordinate entitiesutilize resources allocated by the scheduling entity. BSs 110 are notthe only entities that may function as a scheduling entity. In someexamples, a UE 120 may function as a scheduling entity and may scheduleresources for one or more subordinate entities (e.g., one or more otherUEs 120), and the other UEs 120 may utilize the resources scheduled bythe UE 120 for wireless communication. In some examples, a UE 120 mayfunction as a scheduling entity in a peer-to-peer (P2P) network, and/orin a mesh network. In a mesh network example, UEs 120 may communicatedirectly with one another in addition to communicating with a schedulingentity.

In some examples, the communication between the UEs 120 and BSs 110 isreferred to as the access link. The access link may be provided via a Uuinterface. Communication between devices may be referred as thesidelink.

In some examples, two or more subordinate entities (e.g., UEs 120) maycommunicate with each other using sidelink signals. Real-worldapplications of such sidelink communications may include public safety,proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V)communications, Internet of Everything (IoE) communications, IoTcommunications, mission-critical mesh, and/or various other suitableapplications. Generally, a sidelink signal may refer to a signalcommunicated from one subordinate entity (e.g., UE 120 a) to anothersubordinate entity (e.g., another UE 120) without relaying thatcommunication through the scheduling entity (e.g., UE 120 or BS 110),even though the scheduling entity may be utilized for scheduling and/orcontrol purposes. In some examples, the sidelink signals may becommunicated using a licensed spectrum (unlike wireless local areanetworks, which typically use an unlicensed spectrum). One example ofsidelink communication is PC5, for example, as used in V2V, LTE, and/orNR.

Various sidelink channels may be used for sidelink communications,including a physical sidelink discovery channel (PSDCH), a physicalsidelink control channel (PSCCH), a physical sidelink shared channel(PSSCH), and a physical sidelink feedback channel (PSFCH). The PSDCH maycarry discovery expressions that enable proximal devices to discovereach other. The PSCCH may carry control signaling such as sidelinkresource configurations and other parameters used for datatransmissions, and the PSSCH may carry the data transmissions. The PSFCHmay carry feedback such as CSI related to a sidelink channel quality.

FIG. 3A and FIG. 3B show diagrammatic representations of example V2Xsystems, in accordance with some aspects of the present disclosure. Forexample, the vehicles shown in FIG. 3A and FIG. 3B may communicate viasidelink channels and may perform sidelink CSI reporting as describedherein.

The V2X systems, provided in FIG. 3A and FIG. 3B provide twocomplementary transmission modes. A first transmission mode, shown byway of example in FIG. 3A, involves direct communications (for example,also referred to as sidelink communications) between participants (e.g.,between different UEs) in proximity to one another in a local area.Generally, this first transmission mode may allow participants tocommunicate without communicating through (e.g., sending transmissionsto and/or receiving transmissions from) a network entity, such as agNodeB or base station. A second transmission mode, shown by way ofexample in FIG. 3B, involves network communications through a network,which may be implemented over a Uu interface (for example, a wirelesscommunication interface between a radio access network (RAN) and a UE).

Referring to FIG. 3A, a V2X system 300 (for example, including vehicleto vehicle (V2V) communications) is illustrated with two vehicles 302,304. The first transmission mode allows for direct communication betweendifferent participants in a given geographic location. As illustrated, avehicle can have a wireless communication link 306 with an individual(V2P) (for example, via a UE) through a PC5 interface. Communicationsbetween the vehicles 302 and 304 may also occur through a PC5 interface308. In a like manner, communication may occur from a vehicle 302 toother highway components (for example, highway component 310), such as atraffic signal or sign (V2I) through a PC5 interface 312. With respectto each communication link illustrated in FIG. 3A, two-way communicationmay take place between elements, therefore each element may be atransmitter and a receiver of information. The V2X system 300 may be aself-managed system implemented without assistance from a networkentity. A self-managed system may enable improved spectral efficiency,reduced cost, and increased reliability as network service interruptionsdo not occur during handover operations for moving vehicles. The V2Xsystem may be configured to operate in a licensed or unlicensedspectrum, thus any vehicle with an equipped system may access a commonfrequency and share information. Such harmonized/common spectrumoperations allow for safe and reliable operation.

FIG. 3B shows a V2X system 350 for communication between a vehicle 352and a vehicle 354 through a network entity 356. These networkcommunications may occur through discrete nodes, such as a base station(for example, an eNB or gNB), that sends and receives information to andfrom (for example, relays information between) vehicles 352, 354. Thenetwork communications through vehicle to network (V2N) links 358 and310 may be used, for example, for long range communications betweenvehicles, such as for communicating the presence of a car accident adistance ahead along a road or highway. Other types of communicationsmay be sent by the node to vehicles, such as traffic flow conditions,road hazard warnings, environmental/weather reports, and service stationavailability, among other examples. Such data can be obtained fromcloud-based sharing services.

Example Two-Stage Sidelink Control Information (SCI)

As mentioned above, aspects of the present disclosure relate totechniques for channel estimation for a two-stage sidelink controlinformation (SCI) using sidelink data channel demodulation referencesignals (DMRS).

In certain systems, such as NR systems (e.g., Release 16 NR), atwo-stage SCI is transmitted between user equipment (UEs) in sidelinkcommunications. The two-stage SCI may include a first stage (referred toas SCI-1) and a second stage (referred to as SCI-2).

The SCI-1 may include information regarding resource availability, suchas resource reservation and resource allocation information, andinformation for decoding the SCI-2. The SCI-2 may include at leastinformation for decoding data and information for determining theintended recipient of the transmission. In some aspects, to allow forreceiving devices to determine the intended recipient of the two-stageSCI, the SCI-2 may be modulated using a DMRS associated with a specificreceiving device. That specific receiving device may thus be able tosuccessfully demodulate the SCI-2 and determine that it is the intendedrecipient of the two-stage SCI by having been able to successfullydemodulate the SCI-2; other receiving devices, in contrast, may not beable to demodulate the SCI-2 and may thus determine that they are notthe intended recipient of the two-stage SCI.

FIG. 4 is a diagram illustrating example sidelink data channel DMRS andtwo-stage SCI transmission in a slot 400, in accordance with certainaspects of the present disclosure. In some examples, the Stage 1 Control402 (e.g., SCI-1 in a two-stage SCI transmission) is transmitted overthe physical sidelink control channel (PSCCH), as shown in FIG. 4. Insome examples, the Stage 2 Control 404 (e.g., SCI-2 in the two-stage SCItransmission) may be transmitted over a second PSCCH, as shown in FIG.4. In some examples, however, the SCI-2 may be transmitted (e.g.,piggybacked) on the PSSCH (not shown). Generally, in piggybacking theSCI-2 transmission on the PSSCH, the SCI-2 transmission and othertransmissions, such as data transmissions on the PSSCH, may bemultiplexed for transmission using a same channel.

According to certain aspects, DMRS for the sidelink data channel (e.g.,the PSSCH) is used to demodulate the SCI-2. As discussed, DMRSs may beassociated with specific receiving devices, and the DMRS for thesidelink channel may be used to modulate the SCI-2 at the transmittingdevice. Recipients of the SCI-2 may use their own DMRSs to attempt todemodulate the SCI-2, and the device that successfully demodulates theSCI-2 (e.g., using the DMRS associated with that device) may determinethat the SCI transmission is intended for that device. In some aspects,the PSSCH DMRS may also be used to perform channel estimation for theSCI-2.

In some examples, the PSCCH may use 1 layer (e.g., be transmitted usinga single data stream). However, the PSSCH can be transmitted using morethan 1 layer (e.g., be transmitted using one or multiple data streams).Thus, the sidelink control channel (e.g., a channel on which SCI-1 istransmitted) may use 1 layer and the SCI-2 may use one or multiplelayers (e.g., if the SCI-2 is transmitted on the PSSCH).

Accordingly, techniques and apparatus are desirable for demodulating thesecond stage of the two-part SCI (e.g., the SCI-2) using the datasidelink channel DMRS, for example, even when the second stage of thetwo-part SCI and the data sidelink channel use different numbers oflayers.

Example Channel Estimation for Two-Stage Sidelink Control Using SidelinkData Channel DMRS

As discussed above (e.g., with respect to FIG. 4), sidelink data channeldemodulation reference signals (DMRS) can be used for channel estimationfor a two-stage sidelink control. The second stage (SCI-2) of thetwo-stage sidelink control information can be demodulated based on thephysical sidelink shared channel (PSSCH) DMRS (e.g., based on channelestimation performed using the physical sidelink shared channel (PSSCH)DMRS).

According to certain aspects, the SCI-2 and the PSSCH may share one ormore antenna ports. For example, the SCI-2 may be transmitted using asubset or all of the antenna ports used for the PSCCH. The SCI-2 may useonly antenna ports from the set of antenna ports used for the PSSCH.Because the SCI-2 and the PSSCH may share one or more antenna ports,various properties of the channel on which the SCI-2 is transmitted andthe PSSCH may be similar, and thus, channel estimation performed on onechannel (e.g., using DMRSs transmitted on the PSSCH) may berepresentative of channel conditions on the other channel (e.g., thechannel on which the SCI-2 is transmitted).

According to certain aspects, the PSSCH may be precoded. The precoderfor the PSSCH may be known to both the transmitter and receiver of thePSSCH. In some examples, the user equipment (UE) that that transmits thePSSCH may provide an indication to the receiving UE of the precoder usedfor the PSSCH transmission. For example, the indication of the precoderused for the PSSCH transmission may be indicated to the receiving UEwhen a connection is established, in system information update messages,or in other control information that may be transmitted to the receivingUE (e.g., via one or both of the PSCCH or the PSSCH). The indication ofthe precoder used for the PSSCH transmission may be an implicitindication or an explicit indication. An implicit indication may, forexample, indicate the precoder used for the PSSCH transmission based onsome other information signaled to the receiving UE, while an explicitindication may, for example, include the precoder or an indexidentifying a specific pre-configured precoder that the receiving UE isto use. The receiving UE can use the PSSCH precoder to estimate thechannel and demodulate the SCI-2.

According to certain aspects, the SCI-2 may be transmitted using thelowest index antenna ports of the PSSCH. That is, the SCI-2 may betransmitted using a subset of the antenna ports used for the PSSCH,which may allow for channel estimation performed in respect of the PSSCHto be representative of channel conditions for the channel on which theSCI-2 is transmitted. In some examples, when the PSSCH and the SCI-2 aretransmitted using the number of layers (e.g., using the same number ofdata streams), then the UE may transmit the SCI-2 on the same antennaports as those used for transmitting the PSSCH. For example, if atwo-layer PSSCH is transmitted using ports X000 and X002, then the SCI-2may also be transmitted using ports X000 and X002. In some examples, ifthe SCI-2 has fewer layers than the PSSCH, the SCI-2 may be transmittedusing the lower indexed ports of the ports used for the PSSCH, as thehigher layer ports may generally be unavailable for transmission of theSCI-2 (e.g., due to the codebook used to encode the SCI-2). For example,if the two-layer PSSCH is transmitted using ports X000 and X002, then asingle-layer SCI-2 may be transmitted using the port X000 (e.g., theport having the lower index of the pair of ports X000 and X002).

According to certain aspects, if one of the antenna ports used fortransmitting the PSSCH is a phase tracking reference signal (PT-RS)port, then the SCI-2 may be transmitted using the PT-RS port. BecausePT-RSs may be transmitted in combination with DMRSs, transmitting theSCI-2 on the same port as the port used for transmitting PT-RSs mayallow for channel estimation performed in respect of the PT-RS port tobe representative of channel conditions for the channel (and antennaport(s)) used to transmit the SCI-2. In some cases, the SCI-2 may usefewer layers than the PSSCH. Regardless of the number of layers used bythe SCI-2 and the PSSCH, the SCI-2 may be transmitted using the PT-RSport even if the PT-RS is not the port having the lowest index of theports used for the PSSCH.

According to certain aspects, the UE may be configured with, or receivean indication of, the PSSCH DMRSs that the UE can use for demodulatingthe SCI-2. In some examples, the UE can flexibly determine the PSSCHDMRSs to use for demodulating the SCI-2. In some examples, the UE mayuse PSSCH DMRSs received before the start of the SCI-2 to demodulate theSCI-2. In some examples, the UE may use the PSSCH DMRSs received up tothe end of the SCI-2 to demodulate the SCI-2. In some examples, the UEmay use PSSCH DMRSs received up to the end of the slot to demodulate theSCI-2. In some examples, the UE uses all PSSCH DMRSs to demodulate theSCI-2. Processing timelines may be independent of the PSSCH DMRSs usedfor demodulating SCI-2 or may change based on the PSSCH DMRSs used forthe demodulation.

According to certain aspects, the number of layers for the SCI-2 can beconfigured or indicated (e.g., via explicit or implicit signaling) tothe UE. In some examples, the number of layers for the SCI-2 may beexplicitly signaled to the receiving UE. For example, the number oflayers be explicitly signaled in the SCI-1. In some examples, the numberof layers for the SCI-2 may be implicitly signaled. For example, thenumber of layers may be implicitly determined from DMRSs included in theSCI-1. In some examples, a scrambling seed for the DMRSs in the SCI-1may indicate the number of layers for the SCI-2. Different scramblingseeds may, for example, indicate that a fixed number of layers is usedfor the PSSCH and the SCI-2, the same number of layers as used for thePSSCH, or a different number of layers. In some examples, the number oflayers for the SCI-2 may be a configured (e.g., fixed) number of layers(e.g., such 1 layer). In some examples, the number of layers for theSCI-2 may be number of layers for the PSSCH. In such a case, both thetransmitting and receiving UE may assume or otherwise expect the SCI-2to use the same number of layers as used for the PSSCH. In someexamples, the number layers for the SCI-2 may be configured orpreconfigured.

According to certain aspects, the UE may transmit all channels on thesame OFDM symbol with the same (or within a tolerance range orthreshold) power spectral density (PSD), or transmit power so thatchannel conditions may remain the same for any data carried within thatOFDM symbol and that a receiver may receive different channels carriedon the same OFDM symbol at the same or similar received power level. Insome examples, the UE may apply power control to ensure that thechannels on the symbol are transmitted with the same PSD (or within thetolerance). The transmission of the channels on the OFDM symbol with thesame power level or power levels within a tolerance range or thresholdmay be performed such that the channels transmitted on the same OFDMsymbol are received, at a receiving device (e.g., a UE connected via asidelink channel) at a same or similar (e.g., within a tolerance rangeor threshold) received power level. In some examples, the precoder maybe selected in order to ensure that the same power level, or a powerlevel within the tolerance range or threshold, is used to transmit thechannels on the same OFDM symbol (e.g., to transmit PSCCH and PSSCH).

In some examples, the choice of precoder for the PSSCH may be restrictedto allow for PSSCH and SCI-2 to be transmitted using different numbersof layers while allowing channel estimates performed in respect of DMRSscarried on the PSSCH to be applicable to SCI-2. For example, arestriction placed on the choice of precoder for PSSCH, and also usedfor SCI-2 may specify that the precoder cannot be [1 0; 0 1] if thenumber of layers of SCI-2 and PSSCH is not the same. In this example, aphysical antenna may not be directly mapped to an antenna port.

FIGS. 5-9 are flow diagrams illustrating example operations 500-900 forwireless communication, in accordance with certain aspects of thepresent disclosure. The operations 500-900 may be performed, forexample, by a sidelink UE (e.g., such as a UE 120 a in the wirelesscommunication network 100). Operations 500-900 may be implemented assoftware components that are executed and run on one or more processors(e.g., controller/processor 280 of FIG. 2). Further, the transmissionand reception of signals by the UE in operations 500-900 may be enabled,for example, by one or more antennas (e.g., antennas 252 of FIG. 2). Incertain aspects, the transmission and/or reception of signals by the UEmay be implemented via a bus interface of one or more processors (e.g.,controller/processor 280) obtaining and/or outputting signals.

FIG. 5 is a flow diagram illustrating example operations 500 that may beperformed by a UE for second stage SCI transmission with shared DMRSports, in accordance with certain aspects of the present disclosure.

Operations 500 may begin, at 505, by transmitting one or more DMRSs fora sidelink data channel (e.g., PSSCH) transmission via a set of one ormore antenna ports. In some aspects, the UE may transmit the one or moreDMRSs for the sidelink data channel transmission to a second UE or otherdevice connected to and in communication with the UE via a sidelinkconnection.

At 510, the UE transmits a second stage of a two-stage SCI (e.g., SCI-2)transmission using antenna ports from the set of antenna ports.

In some examples, the two-stage SCI includes a first stage of the SCItransmitted on a first PSCCH and carrying resource availabilityinformation and a second stage of the SCI transmitted on a second PSCCHor on the PSSCH (though using different time resources from the DMRSstransmitted for the sidelink data channel at 505) and carryinginformation to decode a data transmission. In some examples, the firststage SCI and the second stage of the SCI are frequency divisionmultiplexed (FDM) in one or more symbols in a slot (e.g., interleaved),as discussed above with respect to FIG. 4. It should be noted that, atleast in some aspects, the content of the first stage of the two-stageSCI may not be needed in order for the UE to decode the second stage ofthe two-stage SCI, as the second stage of the two-stage SCI may bemodulated (and thus demodulated) based on specific DMRSs.

In some examples, the UE transmits the second stage using one or moreantenna ports having the lowest indices of the set of antenna ports usedfor the sidelink data channel transmission. As discussed above, bytransmitting the second stage of the two-stage SCI using antenna portshaving the lowest indices of the set of antenna ports used for thesidelink data channel transmission, the sidelink data channeltransmission and the second stage of the two-stage SCI may betransmitted using different numbers of layers while allowing for channelestimates performed in respect of the sidelink data channel to berepresentative of channel conditions for the channel used to transmitthe second stage of the two-stage SCI. In some examples, the UEtransmits the second stage using a PT-RS antenna port of the set ofantenna ports used for the sidelink data channel transmission.

In some examples, the UE provides an explicit indication to a receivingdevice (e.g., a second UE or a device connected with the UE via asidelink connection) in a first stage of the SCI of a number of layersof the second stage of the two-stage SCI. In some examples, the UEimplicitly indicates, to the receiving device, a number of layers of thesecond stage of the two-stage SCI (e.g., through an indication of ascrambling seed associated with a specific number of layers used totransmit the second stage of the two-stage SCI).

In some examples, the UE transmits the second stage of the SCI using asingle layer. In some examples, the UE transmits the second stage of theSCI using a number of layers equal to a number of layers used for thesidelink data channel transmission. In some examples, the UE transmitsthe second stage of the SCI using a configured number of layers (e.g., anumber of layers that is configured a priori and indicated to thereceiving UE).

In some examples, the UE transmits the first and second stages of thetwo-stage SCI at a same power level or at power levels within aconfigured tolerance so that the receiving UE receives the first andsecond stages of the two-stage SCI at the same received power level or areceived power level that is within a threshold amount of power fromeach other. In some examples, the UE selects a precoder for the sidelinkdata channel and the second stage of the two-stage SCI to control thepower level. In some examples, the precoder may not directly map anantenna port to a physical antenna when the sidelink data transmissionand the second stage of the two-stage SCI are transmitted using adifferent number of layers.

FIG. 6 is a flow diagram illustrating example operations 600 that may beperformed by a UE for second stage SCI demodulation with shared DMRSports, in accordance with certain aspects of the present disclosure.

The operations 600 may begin, at 605, by receiving one or more DMRSs fora sidelink data channel (e.g., PSSCH) transmission via a set of one ormore antenna ports.

At 610, the UE receives a second stage of a two-stage SCI transmissionusing antenna ports from the set of antenna ports.

In some examples, the two-stage SCI includes a first SCI transmitted ona first PSCCH and carrying resource availability information and asecond SCI transmitted on a second PSCCH or on the PSSCH and carryinginformation to decode a data transmission. In some examples, the firstSCI and the second SCI are FDMed in one or more symbols in a slot (e.g.,interleaved).

In some examples, the UE receives the second stage using one or moreantenna ports having the lowest indices of the set of antenna ports usedfor the sidelink data channel transmission. As discussed above, bytransmitting the second stage of the two-stage SCI using antenna portshaving the lowest indices of the set of antenna ports used for thesidelink data channel transmission, the sidelink data channeltransmission and the second stage of the two-stage SCI may betransmitted using different numbers of layers while allowing for channelestimates performed in respect of the sidelink data channel to berepresentative of channel conditions for the channel used to transmitthe second stage of the two-stage SCI. In some examples, the UE receivesthe second stage using a PT-RS antenna port of the set of antenna portsused for the sidelink data channel transmission.

In some examples, the UE receives an explicit indication in a firststage of the SCI of a number of layers of the second stage of the SCI.In some examples, the UE implicitly determines a number of layers of thesecond stage of the SCI based on a mapping (e.g., through an indicationof a scrambling seed associated with a specific number of layers used totransmit the second stage of the two-stage SCI).

In some examples, the UE receives the second stage of the SCI using asingle layer. In some examples, the UE receives the second stage of theSCI using a number of layers equal to a number of layers used for thesidelink data channel transmission. In some examples, the UE receivesthe second stage of the SCI using a configured number of layers.Generally, the UE may receive the second stage of the SCI using anynumber of layers that allows for channel estimations performed inrespect of the PSSCH to be representative of channel conditions for thechannel on which the second stage of the SCI is received.

In some examples, the sidelink data channel and the first and secondstages of the two-stage SCI are received at a same power level or atpower levels within a configured tolerance.

At 615, the UE demodulates the second stage of the two-stage SCI usingthe one or more DMRSs for the sidelink data channel. In some examples,the UE demodulates the second stage of the two-stage SCI using DMRSsreceived before receiving the start of the second stage of the two-stageSCI, which may allow for the second stage of the two-stage SCI to bedemodulated quickly (e.g., after the second stage of the two-stage SCIis received). In some examples, the UE demodulates the second stage ofthe two-stage SCI using DMRSs received up to receiving the end of thesecond stage of the two-stage SCI, which may allow for the second stageof the two-stage SCI to be demodulated using additional information. Insome examples, the UE demodulates the second stage of the two-stage SCIusing DMRSs received up to the end of a slot in which the second stageof the two-stage SCI is received, which may allow for the second stageof the two-stage SCI to be demodulated using still further additionalinformation. In some examples, the UE demodulates the second stage ofthe two-stage SCI using all DMRSs received for the PSSCH, which mayallow for the second stage of the two-stage SCI to be demodulated usingstill further additional information. In some examples, the UE flexiblydetermines the DMRSs of the sidelink data channel to use fordemodulating the second stage of the two-stage SCI, which may allow forthe UE to balance, for example, the speed at which the second stage ofthe two-stage DMRS is demodulated with the amount of information used todemodulate the second stage of the two-stage SCI.

FIG. 7 is a flow diagram illustrating example operations 700 that may beperformed by a UE for second stage SCI transmission with shared sidelinkdata channel precoder, in accordance with certain aspects of the presentdisclosure.

Operations 700 may begin, at 705, by transmitting one or more DMRSs fora sidelink data channel transmission, the sidelink data channel precodedwith a precoder. The one or more DMRSs may be transmitted, for example,to a second UE or another device connected with the UE via a sidelinkconnection.

At 710, the UE precodes a second stage of a two-stage SCI transmissionusing the precoder. In some examples, the UE provides, to the receivingdevice, an indication or configuration of the precoder used for thesidelink data channel transmission. The indication or configuration ofthe precoder used for the sidelink data channel transmission may becarried in control information, such as information carried in one orboth stages of the two-stage SCI, in information exchanged between UEswhen a sidelink connection is established, in system update information,or the like.

At 715, the UE transmits the precoded second stage of the two-stage SCI.The UE may transmit the precoded second stage of the two-stage SCI tothe second UE or other device connected with the UE via a sidelinkconnection. The UE may also transmit the first stage of the two-stageSCI to the second UE, as discussed above and illustrated in FIG. 4.

FIG. 8 is a flow diagram illustrating example operations 800 that may beperformed by a UE for second stage SCI demodulation with shared sidelinkdata channel precoder, in accordance with certain aspects of the presentdisclosure.

At 805, the UE receives one or more DMRSs for a precoded sidelink datachannel transmission. The UE may receive the one or more DMRSs fromanother UE connected with the UE via a sidelink connection.

At 810, the UE estimates the channel based on the precoded sidelink datachannel transmission (e.g., based on the DMRSs for the precoded sidelinkdata channel transmission). The UE may receive an indication orconfiguration of the precoder used for the sidelink data channeltransmission and estimate the channel based on the indicated orconfigured precoder.

At 815, the UE demodulates a second stage of a two-stage SCItransmission based on the estimation.

FIG. 9 is a flow diagram illustrating example operations 900 that may beperformed by a UE for flexible DMRS determination for second stage SCIdemodulation, in accordance with certain aspects of the presentdisclosure.

Operations 900 may begin, at 905, by receiving one or more DMRSs for asidelink data channel transmission in a slot via a set of one or moreantenna ports. The one or more DMRSs may be received from another UEconnected with the UE via a sidelink connection.

At 910, the UE flexibly determines DMRSs of the one or more DMRSs to usefor demodulating a second stage of a two-stage SCI transmission.

At 915, the UE demodulates the second stage of the two-stage SCI usingthe determined DMRSs for the sidelink data channel.

In some examples, the UE may determine that the second stage of thetwo-stage SCI is to be demodulated using DMRSs received before receivingthe start of the second stage of the two-stage SCI, which may allow forthe second stage of the two-stage SCI to be demodulated quickly (e.g.,after the second stage of the two-stage SCI is received). In someexamples, the UE may determine that the second stage of the two-stageSCI is to be demodulated using DMRSs received up to receiving the end ofthe second stage of the two-stage SCI. In some examples, the UE maydetermine that the second stage of the two-stage SCI may be demodulatedusing DMRSs received up to the end of a slot in which the second stageof the two-stage SCI is received. In some examples, the UE may determinethat the second stage of the two-stage SCI is to be demodulated usingall DMRSs received for the PSSCH. In each of these cases, the secondstage of the two-stage SCI may be demodulated using additionalinformation, which may allow for more accurate decoding of the two-stageSCI.

FIG. 10 is a message flow diagram illustrating example messages that maybe exchanged between a UE 1002 and a receiving device 1004 to performtwo-stage SCI transmissions using shared DMRS ports, in accordance withcertain aspects of the present disclosure.

As illustrated, a UE 1002 may transmit one or more demodulationreference signals (DMRSs) 1010 to the receiving device 1004. Thereceiving device 1004 may be, for example, another UE or other deviceconnected with UE 1002 via a sidelink connection. The DMRSs 1010 may betransmitted to the receiving device 1004 on a data (or shared) channel,such as a PSSCH, and may be used, as discussed above, by the receivingdevice to demodulate the second stage of an SCI.

After transmitting DMRSs 1010, the UE 1002 may transmit a two-stage SCI1012 to the receiving device 1004. The first stage of the two-stage SCImay carry, for example, resource reservation and allocation informationand information that may be used to decode the second stage of thetwo-stage SCI. The second stage of the two-stage SCI may carry, forexample, information needed to decode a data payload carried on the datachannel (e.g., the PSSCH). In some aspects, the UE 1002 may transmit thefirst stage and the second stage of the two-stage SCI 1012 to thereceiving device 1004 using a same transmit power or transmit powersthat are within a threshold difference such that the first stage and thesecond stage of the two-stage SCI are received at similar received powerlevels.

The receiving device 1004 may decode the first stage of the two-stageSCI at block 1014 and the second stage of the two-stage SCI at block1016. The second stage of the two-stage SCI may be decoded at block 1016based on resource information included in the first stage of thetwo-stage SCI and one or more of the DMRSs 1010 transmitted by the UE1002. As discussed above, the receiving device 1004 may use informationabout antenna ports used to transmit the PSSCH, a precoder used for thePSSCH, a number of layers for second stage control and the PSSCH, orother information associated with the DMRSs to decode the second stageof the two-stage SCI.

FIG. 11 illustrates a communications device 1100 that may includevarious components (e.g., corresponding to means-plus-functioncomponents) configured to perform operations for the techniquesdisclosed herein, such as the operations illustrated in FIGS. 5-9. Thecommunications device 1100 includes a processing system 1102 coupled toa transceiver 1108 (e.g., a transmitter and/or a receiver). Thetransceiver 1108 is configured to transmit and receive signals for thecommunications device 1100 via an antenna 1110, such as the varioussignals as described herein. The processing system 1102 may beconfigured to perform processing functions for the communications device1100, including processing signals received and/or to be transmitted bythe communications device 1100.

The processing system 1102 includes a processor 1104 coupled to acomputer-readable medium/memory 1112 via a bus 1106. In certain aspects,the computer-readable medium/memory 1112 is configured to storeinstructions (e.g., computer-executable code) that when executed by theprocessor 1104, cause the processor 1104 to perform the operationsillustrated in FIGS. 5-8, and/or FIG. 9, or other operations forperforming the various techniques discussed herein for channelestimation for sidelink control using sidelink data channel DMRS. Incertain aspects, computer-readable medium/memory 1112 stores code 1114for transmitting and/or receiving DMRS for PSSCH; and code 1116 forsending and/or demodulating the second stage of two-stage SCI using thePSSCH DMRS, in accordance with aspects of the present disclosure. Incertain aspects, the processor 1104 has circuitry configured toimplement the code stored in the computer-readable medium/memory 1112.The processor 1104 includes circuitry 1118 for transmitting and/orreceiving DMRS for PSSCH; and circuitry 1120 for sending and/ordemodulating the second stage of two-stage SCI using the PSSCH DMRS, inaccordance with aspects of the present disclosure.

Example Embodiments

Embodiment 1: A method for wireless communications by a user equipment(UE), comprising: transmitting one or more demodulation referencesignals (DMRS) for a sidelink data channel transmission via a set of oneor more antenna ports; and transmitting a second stage of a two-stagesidelink control information (SCI) transmission using antenna ports fromthe set of antenna ports.

Embodiment 2: The method of Embodiment 1, wherein: the sidelink datachannel transmission comprises a first physical sidelink shared channel(PSSCH) transmission; and the two-stage SCI comprises a first SCItransmitted on a first physical sidelink control channel (PSCCH) andcarrying resource availability information; and a second SCI transmittedon a second PSCCH or on the PSSCH and carrying information to decode adata transmission.

Embodiment 3: The method of Embodiment 2, wherein the first SCI and thesecond SCI are frequency division multiplexed (FDMed) in one or moresymbols in a slot.

Embodiment 4: The method of any of Embodiments 1 to 3, whereintransmitting the second stage of the two-stage SCI comprisestransmitting the second stage using one or more lowest index antennaports of the set of antenna ports used for the sidelink data channeltransmission.

Embodiment 5: The method of any of Embodiments 1 to 4, whereintransmitting the second stage of the two-stage SCI comprisestransmitting the second stage using a phase tracking reference signal(PT-RS) antenna port of the set of antenna ports used for the sidelinkdata channel transmission.

Embodiment 6: The method of any of Embodiments 1 to 5, furthercomprising providing an explicit indication in a first stage of the SCIof a number of layers of the second stage of the SCI.

Embodiment 7: The method of any of Embodiments 1 to 6, furthercomprising implicitly indicating a number of layers of the second stageof the SCI.

Embodiment 8: The method of any of Embodiments 1 to 7, whereintransmitting the second stage of the SCI comprises transmitting thesecond stage of the SCI using a single layer.

Embodiment 9: The method of any of Embodiments 1 to 8, whereintransmitting the second stage of the SCI comprises transmitting thesecond stage of the SCI using a number of layers equal to a number oflayers used for the sidelink data channel transmission.

Embodiment 10: The method of any of Embodiments 1 to 9, whereintransmitting the second stage of the SCI comprises transmitting thesecond stage of the SCI using a configured number of layers.

Embodiment 11: The method of any of Embodiments 1 to 10, wherein thetransmissions on the sidelink data channel and the first and secondstages of the two-stage SCI are transmitted at a same power level or atpower levels within a configured tolerance.

Embodiment 12: The method of Embodiment 11, further comprising selectinga precoder for the sidelink data channel and the second stage of thetwo-stage SCI to control the power level.

Embodiment 13: The method of Embodiment 12, wherein the precoder doesnot directly map an antenna port to a physical antenna when the sidelinkdata transmission and the second stage of the two-stage SCI aretransmitted using a different number of layers.

Embodiment 14, The method of any of Embodiments 1 to 13, wherein: thesidelink data channel is precoded with a precoder, and second stage ofthe two-stage SCI is precoded using the precoder.

Embodiment 15: The method of any of Embodiments 1 to 14, furthercomprising: providing an indication or configuration of the precoderused for the sidelink data channel transmission.

Embodiment 16: A method for wireless communications by a user equipment(UE), comprising: receiving one or more demodulation reference signals(DMRS) for a sidelink data channel transmission via a set of one or moreantenna ports; receiving a second stage of a two-stage sidelink controlinformation (SCI) transmission using antenna ports from the set ofantenna ports; and demodulating the second stage of the two-stage SCIusing the one or more DMRS for the sidelink data channel.

Embodiment 17: The method of Embodiment 16, wherein: the sidelink datachannel transmission comprises a first physical sidelink shared channel(PSSCH) transmission; and the two-stage SCI comprises a first SCItransmitted on a first physical sidelink control channel (PSCCH) andcarrying resource availability information, and a second SCI transmittedon a second PSCCH or on the PSSCH and carrying information to decode adata transmission.

Embodiment 18: The method of Embodiment 17, wherein the first SCI andthe second SCI are frequency division multiplexed (FDM) in one or moresymbols in a slot.

Embodiment 19: The method of any of Embodiments 16 to 18, whereinreceiving the second stage of the two-stage SCI comprises receiving thesecond stage using one or more lowest index antenna ports of the set ofantenna ports used for the sidelink data channel transmission.

Embodiment 20: The method of any of Embodiments 16 to 19, whereinreceiving the second stage of the two-stage SCI comprises receiving thesecond stage using a phase tracking reference signal (PT-RS) antennaport of the set of antenna ports used for the sidelink data channeltransmission.

Embodiment 21: The method of any of Embodiments 16 to 20, whereindemodulating the second stage of the two-stage SCI using the one or moreDMRS for the sidelink data channel comprises demodulating the secondstage of the two-stage SCI using DMRS received before receiving thestart of the second stage of the two-stage SCI.

Embodiment 22: The method of any of Embodiments 16 to 21, whereindemodulating the second stage of the two-stage SCI using the one or moreDMRS for the sidelink data channel comprises demodulating the secondstage of the two-stage SCI using DMRS received up to receiving the endof the second stage of the two-stage SCI.

Embodiment 23: The method of any of Embodiments 16 to 22, whereindemodulating the second stage of the two-stage SCI using the one or moreDMRS for the sidelink data channel comprises demodulating the secondstage of the two-stage SCI using DMRS received up to the end of a slotin which the second stage of the two-stage SCI is received.

Embodiment 24: The method of any of Embodiments 16 to 23, whereindemodulating the second stage of the two-stage SCI using the one or moreDMRS for the sidelink data channel comprises demodulating the secondstage of the two-stage SCI using all DRMS received for the PSSCH.

Embodiment 25: The method of any of Embodiments 16 to 24, furthercomprising flexibly determining the DMRS of the sidelink data channel touse for demodulating the second stage of the two-stage SCI.

Embodiment 26: The method of any of Embodiments 16 to 25, furthercomprising receiving an explicit indication in a first stage of the SCIof a number of layers of the second stage of the SCI.

Embodiment 27: The method of any of Embodiments 16 to 26, furthercomprising implicitly determining a number of layers of the second stageof the SCI based on a mapping.

Embodiment 28: The method of any of Embodiments 16 to 27, whereinreceiving the second stage of the SCI comprises receiving the secondstage of the SCI using a single layer.

Embodiment 29: The method of any of Embodiments 16 to 28, whereinreceiving the second stage of the SCI comprises receiving the secondstage of the SCI using a number of layers equal to a number of layersused for the sidelink data channel transmission.

Embodiment 30: The method of any of Embodiments 16 to 29, whereinreceiving the second stage of the SCI comprises receiving the secondstage of the SCI using a configured number of layers.

Embodiment 31: The method of any of Embodiments 16 to 30, wherein thetransmissions on the sidelink data channel and the first and secondstages of the two-stage SCI are received at a same power level or atpower levels within a configured tolerance.

Embodiment 32: The method of any of Embodiments 16 to 31, wherein: theone or more DMRSs comprise DMRSs for a precoded sidelink data channel,and the method further comprises: estimating the channel based on theprecoded sidelink data channel transmission, wherein the second stage ofthe two-stage SCI is demodulated based on the estimation.

Embodiment 33: The method of Embodiment 32, further comprising:receiving an indication or configuration of the precoder used for thesidelink data channel transmission; and estimating the channel based onthe indicated or configured precoder.

Additional Considerations

The techniques described herein may be used for various wirelesscommunication technologies, such as NR (e.g., 5G NR), 3GPP Long TermEvolution (LTE), LTE-Advanced (LTE-A), code division multiple access(CDMA), time division multiple access (TDMA), frequency divisionmultiple access (FDMA), orthogonal frequency division multiple access(OFDMA), single-carrier frequency division multiple access (SC-FDMA),time division synchronous code division multiple access (TD-SCDMA), andother networks. The terms “network” and “system” are often usedinterchangeably. A CDMA network may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. A TDMA network may implement aradio technology such as Global System for Mobile Communications (GSM).An OFDMA network may implement a radio technology such as NR (e.g. 5GRA), Evolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDMA, etc. UTRA andE-UTRA are part of Universal Mobile Telecommunication System (UMTS). LTEand LTE-A are releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE,LTE-A and GSM are described in documents from an organization named“3rdGeneration Partnership Project” (3GPP). cdma2000 and UMB aredescribed in documents from an organization named “3rdGenerationPartnership Project 2” (3GPP2). NR is an emerging wirelesscommunications technology under development.

In 3GPP, the term “cell” can refer to a coverage area of a Node B (NB)and/or a NB subsystem serving this coverage area, depending on thecontext in which the term is used. In NR systems, the term “cell” andBS, next generation NodeB (gNB or gNodeB), access point (AP),distributed unit (DU), carrier, or transmission reception point (TRP)may be used interchangeably. A BS may provide communication coverage fora macro cell, a pico cell, a femto cell, and/or other types of cells. Amacro cell may cover a relatively large geographic area (e.g., severalkilometers in radius) and may allow unrestricted access by UEs withservice subscription. A pico cell may cover a relatively smallgeographic area and may allow unrestricted access by UEs with servicesubscription. A femto cell may cover a relatively small geographic area(e.g., a home) and may allow restricted access by UEs having anassociation with the femto cell (e.g., UEs in a Closed Subscriber Group(CSG), UEs for users in the home, etc.). A BS for a macro cell may bereferred to as a macro BS. A BS for a pico cell may be referred to as apico BS. A BS for a femto cell may be referred to as a femto BS or ahome BS.

A UE may also be referred to as a mobile station, a terminal, an accessterminal, a subscriber unit, a station, a Customer Premises Equipment(CPE), a cellular phone, a smart phone, a personal digital assistant(PDA), a wireless modem, a wireless communication device, a handhelddevice, a laptop computer, a cordless phone, a wireless local loop (WLL)station, a tablet computer, a camera, a gaming device, a netbook, asmartbook, an ultrabook, an appliance, a medical device or medicalequipment, a biometric sensor/device, a wearable device such as a smartwatch, smart clothing, smart glasses, a smart wrist band, smart jewelry(e.g., a smart ring, a smart bracelet, etc.), an entertainment device(e.g., a music device, a video device, a satellite radio, etc.), avehicular component or sensor, a smart meter/sensor, industrialmanufacturing equipment, a global positioning system device, or anyother suitable device that is configured to communicate via a wirelessor wired medium. Some UEs may be considered machine-type communication(MTC) devices or evolved MTC (eMTC) devices. MTC and eMTC UEs include,for example, robots, drones, remote devices, sensors, meters, monitors,location tags, etc., that may communicate with a BS, another device(e.g., remote device), or some other entity. A wireless node mayprovide, for example, connectivity for or to a network (e.g., a widearea network such as Internet or a cellular network) via a wired orwireless communication link. Some UEs may be consideredInternet-of-Things (IoT) devices, which may be narrowband IoT (NB-IoT)devices.

The methods disclosed herein comprise one or more steps or actions forachieving the methods. The method steps and/or actions may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isspecified, the order and/or use of specific steps and/or actions may bemodified without departing from the scope of the claims.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover a, b, c,a-b, a-c, b-c, and a-b-c, as well as any combination with multiples ofthe same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b,b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

As used herein, the term “determining” encompasses a wide variety ofactions. For example, “determining” may include calculating, computing,processing, deriving, investigating, looking up (e.g., looking up in atable, a database or another data structure), ascertaining and the like.Also, “determining” may include receiving (e.g., receiving information),accessing (e.g., accessing data in a memory) and the like. Also,“determining” may include resolving, selecting, choosing, establishingand the like.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language of the claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. All structural andfunctional equivalents to the elements of the various aspects describedthroughout this disclosure that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims. No claim element is to be construed under the provisions of 35U.S.C. § 112(f) unless the element is expressly recited using the phrase“means for” or, in the case of a method claim, the element is recitedusing the phrase “step for.”

The various operations of methods described above may be performed byany suitable means capable of performing the corresponding functions.The means may include various hardware and/or software component(s)and/or module(s), including, but not limited to a circuit, anapplication specific integrated circuit (ASIC), or processor. Generally,where there are operations illustrated in figures, those operations mayhave corresponding counterpart means-plus-function components withsimilar numbering.

The various illustrative logical blocks, modules and circuits describedin connection with the present disclosure may be implemented orperformed with a general purpose processor, a digital signal processor(DSP), an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA) or other programmable logic device (PLD),discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any commercially available processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

If implemented in hardware, an example hardware configuration maycomprise a processing system in a wireless node. The processing systemmay be implemented with a bus architecture. The bus may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system and the overall design constraints.The bus may link together various circuits including a processor,machine-readable media, and a bus interface. The bus interface may beused to connect a network adapter, among other things, to the processingsystem via the bus. The network adapter may be used to implement thesignal processing functions of the PHY layer. In the case of a userterminal 120 (see FIG. 1), a user interface (e.g., keypad, display,mouse, joystick, etc.) may also be connected to the bus. The bus mayalso link various other circuits such as timing sources, peripherals,voltage regulators, power management circuits, and the like, which arewell known in the art, and therefore, will not be described any further.The processor may be implemented with one or more general-purpose and/orspecial-purpose processors. Examples include microprocessors,microcontrollers, DSP processors, and other circuitry that can executesoftware. Those skilled in the art will recognize how best to implementthe described functionality for the processing system depending on theparticular application and the overall design constraints imposed on theoverall system.

If implemented in software, the functions may be stored or transmittedover as one or more instructions or code on a computer readable medium.Software shall be construed broadly to mean instructions, data, or anycombination thereof, whether referred to as software, firmware,middleware, microcode, hardware description language, or otherwise.Computer-readable media include both computer storage media andcommunication media including any medium that facilitates transfer of acomputer program from one place to another. The processor may beresponsible for managing the bus and general processing, including theexecution of software modules stored on the machine-readable storagemedia. A computer-readable storage medium may be coupled to a processorsuch that the processor can read information from, and write informationto, the storage medium. In the alternative, the storage medium may beintegral to the processor. By way of example, the machine-readable mediamay include a transmission line, a carrier wave modulated by data,and/or a computer readable storage medium with instructions storedthereon separate from the wireless node, all of which may be accessed bythe processor through the bus interface. Alternatively, or in addition,the machine-readable media, or any portion thereof, may be integratedinto the processor, such as the case may be with cache and/or generalregister files. Examples of machine-readable storage media may include,by way of example, RAM (Random Access Memory), flash memory, ROM (ReadOnly Memory), PROM (Programmable Read-Only Memory), EPROM (ErasableProgrammable Read-Only Memory), EEPROM (Electrically ErasableProgrammable Read-Only Memory), registers, magnetic disks, opticaldisks, hard drives, or any other suitable storage medium, or anycombination thereof. The machine-readable media may be embodied in acomputer-program product.

A software module may comprise a single instruction, or manyinstructions, and may be distributed over several different codesegments, among different programs, and across multiple storage media.The computer-readable media may comprise a number of software modules.The software modules include instructions that, when executed by anapparatus such as a processor, cause the processing system to performvarious functions. The software modules may include a transmissionmodule and a receiving module. Each software module may reside in asingle storage device or be distributed across multiple storage devices.By way of example, a software module may be loaded into RAM from a harddrive when a triggering event occurs. During execution of the softwaremodule, the processor may load some of the instructions into cache toincrease access speed. One or more cache lines may then be loaded into ageneral register file for execution by the processor. When referring tothe functionality of a software module below, it will be understood thatsuch functionality is implemented by the processor when executinginstructions from that software module.

Also, any connection is properly termed a computer-readable medium. Forexample, if the software is transmitted from a website, server, or otherremote source using a coaxial cable, fiber optic cable, twisted pair,digital subscriber line (DSL), or wireless technologies such as infrared(IR), radio, and microwave, then the coaxial cable, fiber optic cable,twisted pair, DSL, or wireless technologies such as infrared, radio, andmicrowave are included in the definition of medium. Disk and disc, asused herein, include compact disc (CD), laser disc, optical disc,digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disksusually reproduce data magnetically, while discs reproduce dataoptically with lasers. Thus, in some aspects computer-readable media maycomprise non-transitory computer-readable media (e.g., tangible media).In addition, for other aspects computer-readable media may comprisetransitory computer-readable media (e.g., a signal). Combinations of theabove should also be included within the scope of computer-readablemedia.

Thus, certain aspects may comprise a computer program product forperforming the operations presented herein. For example, such a computerprogram product may comprise a computer-readable medium havinginstructions stored (and/or encoded) thereon, the instructions beingexecutable by one or more processors to perform the operations describedherein, for example, instructions for performing the operationsdescribed herein and illustrated in FIGS. 5-9.

Further, it should be appreciated that modules and/or other appropriatemeans for performing the methods and techniques described herein can bedownloaded and/or otherwise obtained by a user terminal and/or basestation as applicable. For example, such a device can be coupled to aserver to facilitate the transfer of means for performing the methodsdescribed herein. Alternatively, various methods described herein can beprovided via storage means (e.g., RAM, ROM, a physical storage mediumsuch as a compact disc (CD) or floppy disk, etc.), such that a userterminal and/or base station can obtain the various methods uponcoupling or providing the storage means to the device. Moreover, anyother suitable technique for providing the methods and techniquesdescribed herein to a device can be utilized.

It is to be understood that the claims are not limited to the preciseconfiguration and components illustrated above. Various modifications,changes and variations may be made in the arrangement, operation anddetails of the methods and apparatus described above without departingfrom the scope of the claims.

1. A method for wireless communications by a user equipment (UE),comprising: transmitting one or more demodulation reference signals(DMRSs) for a sidelink data channel transmission via a set of one ormore antenna ports; and transmitting a second stage of a two-stagesidelink control information (SCI) transmission using antenna ports fromthe set of one or more antenna ports.
 2. The method of claim 1, wherein:the sidelink data channel transmission comprises a first physicalsidelink shared channel (PSSCH) transmission; and the two-stage SCIcomprises: a first SCI transmitted on a physical sidelink controlchannel (PSCCH) and carrying resource availability information; and asecond SCI transmitted on the PSSCH and carrying information to decode adata transmission.
 3. The method of claim 2, wherein the first SCI andthe second SCI are frequency division multiplexed (FDMed) in one or moresymbols in a slot.
 4. The method of claim 1, further comprisingproviding an explicit indication to in a first stage of the SCI of anumber of layers of the second stage of the SCI.
 5. The method of claim1, further comprising implicitly indicating a number of layers of thesecond stage of the SCI.
 6. The method of claim 1, wherein transmittingthe second stage of the SCI comprises transmitting the second stage ofthe SCI using a single layer.
 7. The method of claim 1, whereintransmitting the second stage of the SCI comprises transmitting thesecond stage of the SCI using a number of layers equal to a number oflayers used for the sidelink data channel transmission.
 8. The method ofclaim 1, wherein the transmissions on the sidelink data channel, a firststage of the two-stage SCI, and the second stage of the two-stage SCIare transmitted at a same power level or at power levels within aconfigured tolerance.
 9. The method of claim 8, wherein the same powerlevel or the power levels within a configured tolerance comprise powerlevels resulting in reception of the sidelink data channel, a firststage of the two-stage SCI, and the second stage of the two-stage SCI ata same received power level or received power levels within theconfigured tolerance.
 10. The method of claim 8, further comprisingselecting a precoder for the sidelink data channel and the second stageof the two-stage SCI to control the power level.
 11. The method of claim1, wherein: the sidelink data channel is precoded with a precoder; andthe method further comprises precoding the second stage of the two-stagesidelink control information (SCI) transmission using the precoder. 12.A method for wireless communications by a user equipment (UE),comprising: receiving, on a sidelink channel, one or more demodulationreference signals (DMRSs) for a sidelink data channel transmission via aset of one or more antenna ports; receiving a second stage of atwo-stage sidelink control information (SCI) transmission from usingantenna ports from the set of one or more antenna ports; anddemodulating the second stage of the two-stage SCI using the one or moreDMRSs for the sidelink data channel transmission.
 13. The method ofclaim 12, wherein: the sidelink data channel transmission comprises afirst physical sidelink shared channel (PSSCH) transmission; and thetwo-stage SCI comprises: a first SCI transmitted on a physical sidelinkcontrol channel (PSCCH) and carrying resource availability information;and a second SCI transmitted on the PSSCH and carrying information todecode a data transmission.
 14. The method of claim 13, wherein thefirst SCI and the second SCI are frequency division multiplexed (FDMed)in one or more symbols in a slot.
 15. The method of claim 12, whereindemodulating the second stage of the two-stage SCI using the one or moreDMRSs for the sidelink data channel comprises demodulating the secondstage of the two-stage SCI using DMRSs received up to receiving an endof the second stage of the two-stage SCI.
 16. The method of claim 12,wherein demodulating the second stage of the two-stage SCI using the oneor more DMRSs for the sidelink data channel comprises demodulating thesecond stage of the two-stage SCI using DMRSs received up to an end of aslot in which the second stage of the two-stage SCI is received.
 17. Themethod of claim 12, further comprising flexibly determining the one ormore DMRSs of the sidelink data channel to use for demodulating thesecond stage of the two-stage SCI.
 18. The method of claim 12, furthercomprising receiving an explicit indication in a first stage of the SCIof a number of layers used for the second stage of the SCI.
 19. Themethod of claim 12, wherein receiving the second stage of the SCIcomprises receiving the second stage of the SCI using a single layer.20. The method of claim 12, wherein receiving the second stage of theSCI comprises receiving the second stage of the SCI using a number oflayers equal to a number of layers used for the sidelink data channeltransmission.
 21. The method of claim 12, wherein the transmissions onthe sidelink data channel, a first stage of the two-stage SCI, and thesecond stage of the two-stage SCI are received at a same power level orat power levels within a configured tolerance.
 22. The method of claim12, wherein: the one or more DMRSs comprise DMRSs for a precodedsidelink data channel transmission; and the method further comprisesestimating the channel based on the DMRSs for the precoded sidelink datachannel transmission, wherein the second stage of the two-stage SCI isdemodulated based on the estimation.
 23. An apparatus for wirelesscommunications by a user equipment (UE), comprising: a memory; and atleast one processor coupled with the memory and configured to: transmitone or more demodulation reference signals (DMRSs) for a sidelink datachannel transmission via a set of one or more antenna ports, andtransmit a second stage of a two-stage sidelink control information(SCI) transmission using antenna ports from the set of one or moreantenna ports.
 24. The apparatus of claim 23, wherein: the sidelink datachannel transmission comprises a first physical sidelink shared channel(PSSCH) transmission; and the two-stage SCI comprises: a first SCItransmitted on a physical sidelink control channel (PSCCH) and carryingresource availability information; and a second SCI transmitted on thePSSCH and carrying information to decode a data transmission.
 25. Theapparatus of claim 24, wherein the first SCI and the second SCI arefrequency division multiplexed (FDMed) in one or more symbols in a slot.26. The apparatus of claim 23, wherein the processor is furtherconfigured to provide an explicit indication to in a first stage of theSCI of a number of layers of the second stage of the SCI.
 27. Theapparatus of claim 23, wherein the processor is further configured toimplicitly indicate a number of layers of the second stage of the SCI.28. The apparatus of claim 23, wherein the apparatus is configured totransmit the second stage of the SCI by transmitting the second stage ofthe SCI using a single layer.
 29. The apparatus of claim 23, wherein theapparatus is configured to transmit the second stage of the SCI bytransmitting the second stage of the SCI using a number of layers equalto a number of layers used for the sidelink data channel transmission.30. The apparatus of claim 23, wherein the transmissions on the sidelinkdata channel, a first stage of the two-stage SCI, and the second stageof the two-stage SCI are transmitted at a same power level or at powerlevels within a configured tolerance.
 31. The apparatus of claim 30,wherein the same power level or the power levels within a configuredtolerance comprise power levels resulting in reception of the sidelinkdata channel, a first stage of the two-stage SCI, and the second stageof the two-stage SCI at a same received power level or received powerlevels within the configured tolerance.
 32. The apparatus of claim 30,wherein the processor is further configured to select a precoder for thesidelink data channel and the second stage of the two-stage SCI tocontrol the power level.
 33. The apparatus of claim 23, wherein: thesidelink data channel is precoded with a precoder; and the processor isfurther configured to precode the second stage of the two-stage sidelinkcontrol information using the precoder.
 34. An apparatus for wirelesscommunications by a user equipment (UE), comprising: a memory; and atleast one processor coupled with the memory and configured to: receive,on a sidelink channel, one or more demodulation reference signals(DMRSs) for a sidelink data channel transmission via a set of one ormore antenna ports; receive a second stage of a two-stage sidelinkcontrol information (SCI) transmission using antenna ports from the setof antenna ports; and demodulate the second stage of the two-stage SCIusing the one or more DMRSs for the sidelink data channel transmission.35. The apparatus of claim 34, wherein: the sidelink data channeltransmission comprises a first physical sidelink shared channel (PSSCH)transmission; and the two-stage SCI comprises: a first SCI transmittedon a physical sidelink control channel (PSSCH) and carrying resourceavailability information; and a second SCI transmitted on the PSSCH andcarrying information to decode a data transmission.
 36. The apparatus ofclaim 35, wherein the first SCI and the second SCI are frequencydivision multiplexed (FDMed) in one or more symbols in a slot.
 37. Theapparatus of claim 34, wherein the processor is configured to demodulatethe second stage of the two-stage SCI using the one or more DMRSs forthe sidelink data channel by demodulating the second stage of thetwo-stage SCI using DMRSs received up to receiving an end of the secondstage of the two-stage SCI.
 38. The apparatus of claim 34, wherein theprocessor is configured to demodulate the second stage of the two-stageSCI using the one or more DMRSs for the sidelink data channel bydemodulating the second stage of the two-stage SCI using DMRSs receivedup to an end of a slot in which the second stage of the two-stage SCI isreceived.
 39. The apparatus of claim 34, wherein the processor isfurther configured to flexibly determine the one or more DMRSs of thesidelink data channel to use for demodulating the second stage of thetwo-stage SCI.
 40. The apparatus of claim 34, wherein the processor isfurther configured to receive an explicit indication in a first stage ofthe SCI of a number of layers used for the second stage of the SCI. 41.The apparatus of claim 34, wherein the processor is configured toreceive the second stage of the SCI by receiving the second stage of theSCI using a single layer.
 42. The apparatus of claim 34, wherein theprocessor is configured to receive the second stage of the SCI byreceiving the second stage of the SCI using a number of layers equal toa number of layers used for the sidelink data channel transmission. 43.The apparatus of claim 34, wherein the transmissions on the sidelinkdata channel, a first stage of the two-stage SCI, and the second stageof the two-stage SCI are received at a same power level or at powerlevels within a configured tolerance.
 44. The apparatus of claim 34,wherein: the one or more DMRSs comprise DMRSs for a precoded sidelinkdata channel transmission, and the processor is further configured toestimate the channel based on the DMRSs for the precoded sidelink datachannel transmission, wherein the second stage of the two-stage SCI isdemodulated based on the estimation.
 45. An apparatus for wirelesscommunications by a user equipment (UE), comprising: means fortransmitting one or more demodulation reference signals (DMRSs) for asidelink data channel transmission via a set of one or more antennaports; and means for transmitting a second stage of a two-stage sidelinkcontrol information (SCI) transmission using antenna ports from the setof antenna ports.
 46. An apparatus for wireless communications by a userequipment (UE), comprising: means for receiving, on a sidelink channel,one or more demodulation reference signals (DMRSs) for a sidelink datachannel transmission via a set of one or more antenna ports; means forreceiving a second stage of a two-stage sidelink control information(SCI) transmission using antenna ports from the set of antenna ports;and means for demodulating the second stage of the two-stage SCI usingthe one or more DMRSs for the sidelink data channel.
 47. Acomputer-readable medium storing executable code thereon which, whenexecuted by a processor, performs an operation for wirelesscommunications by a user equipment (UE) comprising: transmitting one ormore demodulation reference signals (DMRSs) for a sidelink data channeltransmission via a set of one or more antenna ports; and transmitting asecond stage of a two-stage sidelink control information (SCI)transmission using antenna ports from the set of antenna ports.
 48. Acomputer readable medium storing computer executable code thereon which,when executed by a processor, performs an operation for wirelesscommunications by a user equipment (UE) comprising: receiving one ormore demodulation reference signals (DMRSs) for a sidelink data channeltransmission via a set of one or more antenna ports; code for receivinga second stage of a two-stage sidelink control information (SCI)transmission using antenna ports from the set of antenna ports; and codefor demodulating the second stage of the two-stage SCI using the one ormore DMRS for the sidelink data channel.